1. Field of the Invention
The present invention relates to a functional styrene-butadiene copolymer.
2. Description of Related Art
In general, styrene-butadiene copolymers or styrene-butadiene-polar monomer copolymers are mainly prepared by emulsion copolymerization. These copolymers are used for tires, coating materials, toners, etc. Methods for preparing styrene-butadiene copolymers or styrene-butadiene-polar monomer copolymer by the emulsion copolymerization technique have been disclosed in many patents. For example, U.S. Pat. Nos. 3,575,913 and 3,563,946 disclose preparation of styrene-butadiene or styrene-butadiene-acrylate copolymer in emulsion state using potassium persulfate or azobisisobutyronitrile. U.S. Pat. No. 4,064,081 describes emulsion polymerization of butadiene-styrene copolymer, wherein potassium persulfate is used as a polymerization initiator. U.S. Pat. Nos. 5,274,027 and 5,302,655 describe emulsion polymerization of styrene-butadiene-acrylate copolymer using itaconic acid, methyl methacrylic acid, etc. as an acrylate compound and using ammonium persulfate, etc. as an initiator.
And, U.S. Pat. Nos. 6,512,053 and 6,716,925 describe emulsion polymerization of styrene-butadiene-acrylate copolymer using a hydroxy alkyl acrylate such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, hydroxymethyl(meth)acrylamide, etc., as an acrylate compound and using ammonium persulfate, etc., as an initiator.
These styrene-butadiene copolymers prepared by emulsion polymerization have poor silica compatibility. To improve the silica compatibility, introduction of a carboxylic acid such as acrylic acid is required. However, vinyl carboxylic acid monomers react slowly and change acidity thereby interrupting micelle formation. In addition, removal of residual monomer is restricted. The monomer content needs to be increased to improve the silica compatibility. However, this leads to difficulty in processing the blend, and, as a result, the product has very high viscosity and hardness.
In the tire industries, demands on new styrene-butadiene rubber having polar groups and silica composite adequate for manufacturing silica tires are increasing.